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Backflow & Cross Connections

A backflow is the unwanted and undesirable flow of non-potable water or other liquids back into the water supply system from a consumer's premises.

There are three main causes of backflows. They happen when:

  • There is a sudden drop in mains pressure that causes the water to siphon back into the system.
  • The water supply is directly connected to equipment, such as a boiler or a private bore, which is at a higher pressure than the water supply system. This forces water back into the supply system.
  • A break in the water main sets up a vacuum or partial vacuum in the pipes, sucking liquids in. The same effect can be produced by heavy demand from firefighting or from flushing the pipes.

There are a surprisingly wide range of direct connections to the water supply system from which liquids can be drawn into the water supply system.

These include:

  • air conditioners
  • boilers
  • cooling systems
  • dishwashers
  • hospital equipment
  • laboratory equipment
  • swimming pools
  • private bores
  • washing machines
  • Vet Clinics
  • Mortuaries

Besides these there are a range of fixtures with submerged inlets and the temporary connection of sprays, tanks, and pools and fish ponds.

Below is a backflow manifold similar to those that have been installed since 1997 to new connections. Every connection in the City has now been fitted with these devices. This device is suitable to protect against a "Low Hazard".

Backflow prevention manifold:

Water Manifold


The Risks of Backflow

It is all well and good to treat water to the highest standard at the treatment plant, but it could all be to no avail if it gets contaminated in the pipes which carry it to your home.

Yet that is the risk. Sometimes water can flow into, rather than out of, the tap.

Backflows do not happen very often but the risk is potentially extreme. It may cause wide spread illness through drinking contaminated water. This may also be very costly to rectify to bring the quality of water back to a potable standard.

Since 1997, all new properties in Tauranga have had to have a backflow prevention device fitted to their water supplies. Now, backflow manifolds have been fitted to all the other properties in the city at the same time as the new water meters are installed or replaced. Other higher hazards are identified through city-wide surveys and, if required, property owners will be advised that a higher level of protection is required.

Last Reviewed: 28/03/2017